Polymers with high levels of fluorine have novel properties including chemical and thermal resistance. The commercialization of proton exchange membrane fuel cells (PEMFCs) has been delayed due to the lack of a highly efficient and durable membrane material that can withstand the harsh fuel cell operating conditions. The current PEM standard is a perfluoroalkylsulfonic acid, Nafion®, which displays chemical stability, mechanical resistance and a high ionic conductivity of 0.1 S/cm at 80° C. and fully humidified conditions. Nafion®'s attractive PEM properties result from its well-studied nanophase-separated morphology comprising hydrophilic and hydrophobic domain. Higher temperature operation (≧100° C.) for PEMFCs is advantageous due to faster electrode kinetics of O2 reduction, improved CO tolerance of the catalyst, elimination of cathode side flooding at high current throughput, and reduced radiator size in automobiles. However, utility of Nafion® at higher temperatures and low relative humidity (≦50%) is limited due to the drastic reduction of its proton conductivity resulting from dehydration, its compromised mechanical strength, and its susceptibility to oxidative degradation by peroxide-derived free radicals formed under FC operation. Moreover, the proton-conducting hydrophilic domains in Nafion®'s structure change unpredictably with changes in relative humidity and temperature. Therefore, control of proton conductivity and stability in PEMs are key factors being investigated to obtain robust membranes at high temperature and low relative humidity. The relationship between the proton conductivity and membrane stability often leads to a trade-off, which has become a major problem in PEM development. One approach that has been investigated is the use of well-ordered block copolymers that self-assemble into nanophases. Several copolymer systems, such as sulfonated polysulfone-PVDF, poly(arylene ether sulfone)/(sulfonated polybutadiene), polysulfonated (styrene-butadiene), and sulfonated poly(styrene-isobutylene-styrene), have been reported.
Perfluorocyclic polymers are known to display thermal/oxidative stability, durability, optical transparency, and processability. The facile polymerization through a thermal [2π+2π] cycloaddition of the trifluorovinyloxyether monomers affords the wide applicability of these polymers, including, gas separations and fuel cell membranes. However, with the use of perfluorocyclopentenyl (PFCP) monomer, the production of the resulting hompolymer, copolymer or terpolymer is cheaper than alternate monomers at least in part due to the lack of need of high pressure equipment. Furthermore, handling of PFCP monomer is safer, thereby making the synthesis of the polymer safer as well. Therefore, it would be desirable to sulfonate perfluorocyclic polymers such as PFCP for use in the manufacture of PEM membranes and other desired applications.